A unique characteristic of resident vascular smooth muscle cells (SMCs) and a hallmark of vascular disease progression is SMC phenotypic switching marked by a change in SMC phenotype. Regulation of PTEN, a lipid and protein phosphatase that predominantly inhibits cytoplasmic PI3K/Akt activity, is critical in pathological vascular remodeling. PTEN represses SMC phenotypic switching while its loss results in decreased SM contractile gene expression and increased proliferation and production inflammatory mediators. Enhanced proliferation and inflammatory mediator production are dependent on loss of PTEN's phosphatase activity and consequent increased Akt activity. However, since SM genes are under direct transcriptional control by serum response factor (SRF), the mechanism underlying PTEN's regulation of SM gene expression remained unclear and is the focus of this proposal. Under physiological conditions, SMCs express a quiescent, differentiated phenotype, characterized by high expression of SRF-dependent SM genes. SRF is a ubiquitous and essential transcription factor that binds CArG elements in SM genes. Paradoxically, SRF also regulates immediate early genes. Control of SM gene expression by SRF involves interactions between SRF and cell-specific co- activators, epigenetic control of gene expression, and regulation of SRF through post-translational modifications and spatial/temporal changes. Our new published and preliminary data show a direct link between PTEN and SRF in this regulation. Our published studies demonstrated that PTEN is a downstream effector of SRF through a microRNA (miRNA)-dependent pathway. Loss of this axis promotes reprogramming to a proliferative, inflammatory phenotype. To support this current project, new preliminary data suggest a novel upstream function for nuclear PTEN that is independent of its phosphatase activity. We demonstrate direct interaction of PTEN with SRF, which facilitates SRF-dependent SM gene transcription suggesting a positive feedback loop involving PTEN and SRF. Pathophysiologic or genetic loss of PTEN results in loss of SRF binding to SM gene promoters and SMC phenotypic switching. Clinically, loss of nuclear PTEN and overall decreased expression is observed in intimal SMCs of human atherosclerotic lesions, supporting a critical role for nuclear PTEN in regulation of lesion progression. We propose a positive feedback loop between PTEN and SRF underlies maintenance of a differentiated, quiescent SMC phenotype. We hypothesize that physiologic or pathologic stimuli induce nuclear exclusion of PTEN and SRF with subsequent inhibition of SRF- dependent SM gene transcription and dysregulation of the SRF-miRNA-PTEN network controlling proliferation and inflammation. We will define the molecular mechanisms underlying PTEN regulation of SRF transcriptional activity (Aim One), establish the importance of PTEN-dependent regulation of SRF transcriptional activity using complex genetic mouse models of atherosclerosis and vascular injury (Aim Two), and establish the significance of nuclear PTEN on SMC phenotype in normal and diseased human arteries (Aim Three).
The studies in this proposal are focused on testing a novel role for the signaling molecule, PTEN, in regulating the activity of serum response factor (SRF), which is a master transcriptional regulator of vascular smooth muscle (SMC) phenotype. Changes in SMC phenotype are critical to the progression of vascular diseases such as atherosclerosis, a chronic inflammatory disease that progresses to complicated, unstable arterial lesions, and restenosis, an acute inflammatory disease and major limitation of angioplasty procedures. This project includes studies using cultured SMCs to define the molecular mechanism underlying PTEN's effects on SRF activity, studies using mouse models of atherosclerosis and restenosis using complex genetic models to establish the importance of PTEN-dependent regulation of SRF, and studies using normal and diseased human arteries to validate critical findings from preclinical mouse studies with human disease. Our findings will be highly relevant with the potential to develop novel therapeutics aimed at preserving the mature SMC phenotype for purposes such as stabilization of atherosclerotic lesions and inhibition of in-stent restenosis.
|Ambardekar, Amrut V; Weiser-Evans, Mary C M; Li, Marcella et al. (2018) Coronary Artery Remodeling and Fibrosis With Continuous-Flow Left Ventricular Assist Device Support. Circ Heart Fail 11:e004491|
|Moulton, Karen S; Li, Marcella; Strand, Keith et al. (2018) PTEN deficiency promotes pathological vascular remodeling of human coronary arteries. JCI Insight 3:|
|Weiser-Evans, Mary C M (2017) Smooth Muscle Differentiation Control Comes Full Circle: The Circular Noncoding RNA, circActa2, Functions as a miRNA Sponge to Fine-Tune ?-SMA Expression. Circ Res 121:591-593|
|Horita, Henrick; Wysoczynski, Christina L; Walker, Lori A et al. (2016) Nuclear PTEN functions as an essential regulator of SRF-dependent transcription to control smooth muscle differentiation. Nat Commun 7:10830|